Numerical Investigation of Effects of Different Hub Tip Diameter Ratios on Aerodynamic Performance of Single Shaft Multistage Centrifugal Compression Systems

2012 ◽  
Author(s):  
Thomas Ceyrowsky ◽  
Andre Hildebrandt
Keyword(s):  
Characteristic Curve ◽  
Design Flow ◽  
Flow Coefficient ◽  
Low Flow ◽  
Design Stage ◽  
Daily Routine ◽  
Stage Design ◽  
Design Point ◽  
Thermodynamic Behaviour ◽  
The Impact

Regarding industrial centrifugal compressors in single shaft design, different configurations with e.g. varying numbers of stages or diverse circumferential speeds, necessitate different shaft diameters. Thus the application of impellers with different hub/tip ratios (dh/d2) is daily routine in industrial practice. Increasing hub/tip ratio leads to higher radii and therefore higher relative speeds, to a reduction in the impeller’s meridional length and hence more rapid diffusion, and to a sharper bending from axial to radial direction. In this paper the impact of hub/tip ratio on stage performance is investigated for three different centrifugal compressor stages, by steady state CFD-calculations. The hub/tip ratio is varied between 0.325 < dh/d2 < 0.45. The relation between design stage flow coefficient and hub/tip ratio is also analysed, both at design and off-design. Thermodynamic behaviour is assessed by 1D-data and also by the investigation of secondary flow features. The current analysis shows, that hub/tip ratio’s influence on characteristics is strongly dependent on the particular stage’s design flow coefficient and circumferential Mach-Number. Increasing a high flow stage’s hub/tip ratio is shown to decrease peak efficiency as well, as to limit the operating range. On the contrary, in case of a low flow stage, design point efficiency is hardly affected, but the characteristic curve is tilted around design point, by applying a different hub/tip ratio. However severity of hub/tip ratio’s impact on thermodynamic behaviour shows to decrease together with stage design flow coefficient.

Experimental Investigation and Characterization of the Rotating Stall in a High Pressure Centrifugal Compressor: Part II — Influence of Diffuser Geometry on Stage Performance

2002 ◽  
Author(s):  
G. Ferrara ◽  
L. Ferrari ◽  
C. P. Mengoni ◽  
M. De Lucia ◽  
L. Baldassarre
Keyword(s):  
Experimental Tests ◽  
Rotating Stall ◽  
Geometric Parameters ◽  
Flow Coefficient ◽  
Low Flow ◽  
Main Task ◽  
Stage Performance ◽  
The Impact ◽  
Prediction Criteria

Extensive research on centrifugal compressors has been planned. The main task of the research is to improve present prediction criteria coming from the literature with particular attention to low flow coefficient impellers (low width to radius ratios) where they are no more valid. Very little data has been published for this kind of stages, especially for the last stage configuration (with discharge volute). Many experimental tests have been planned to investigate different configurations. A simulated stage with a backward channel upstream, a 2D impeller with a vaneless diffuser and a constant cross section volute downstream constitute the basic configuration. Several diffuser types with different widths, pinch shapes and diffusion ratios were tested. The effect of geometric parameters on stage stability has been discussed inside part I of the present work; the purpose of this part of the work is to illustrate the effect of the same geometric parameters on stage performance and to quantify the impact of stability improvements on stage losses.

Reynolds Number and Roughness Effects on Turbocompressor Performance: Numerical Calculations and Measurement Data Evaluation

2020 ◽  
Author(s):  
Fabian Dietmann ◽  
Michael Casey ◽  
Damian M. Vogt
Keyword(s):  
Reynolds Number ◽  
Measurement Data ◽  
Theoretical Models ◽  
Design Flow ◽  
Flow Coefficient ◽  
Low Flow ◽  
Roughness Effects ◽  
Flow Channels ◽  
Compressor Performance ◽  
Low Flow Coefficient

Abstract Further validation of an analytic method to calculate the influence of changes in Reynolds number, machine size and roughness on the performance of axial and radial turbocompressors is presented. The correlation uses a dissipation coefficient as a basis for scaling the losses with changes in relative roughness and Reynolds number. The original correlation from Dietmann and Casey [6] is based on experimental data and theoretical models. Evaluations of five numerically calculated compressor stages at different flow coefficients are presented to support the trends of the correlation. It is shown that the sensitivity of the compressor performance to Reynolds and roughness effects is highest for low flow coefficient radial stages and steadily decreases as the design flow coefficient of the stage and the hydraulic diameter of the flow channels increases.

scholarly journals Design of a Wide-Range Centrifugal Compressor Stage for Supercritical CO2 Power Cycles

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Robert Pelton ◽  
Sewoong Jung ◽  
Tim Allison ◽  
Natalie Smith
Keyword(s):  
Operating Conditions ◽  
Low Flow ◽  
Inlet Temperature ◽  
Compressor Stage ◽  
Stage Design ◽  
Power Cycles ◽  
Design Point ◽  
Operating Range ◽  
Wide Range ◽  
Compressor Efficiency

Supercritical carbon dioxide (sCO2) power cycles require high compressor efficiency at both the design point and over a wide operating range. Increasing the compressor efficiency and range helps maximize the power output of the cycle and allows operation over a broader range of transient and part-load operating conditions. For sCO2 cycles operating with compressor inlets near the critical point, large variations in fluid properties are possible with small changes in temperature or pressure. This leads to particular challenges for air-cooled cycles where compressor inlet temperature and associated fluid density are subject to daily and seasonal variations as well as transient events. Design and off-design operating requirements for a wide-range compressor impeller are presented where the impeller is implemented on an integrally geared compressor–expander concept for a high temperature sCO2 recompression cycle. In order to satisfy the range and efficiency requirements of the cycle, a novel compressor stage design incorporating a semi-open impeller concept with a passive recirculating casing treatment is presented that mitigates inducer stall and extends the low flow operating range. The stage design also incorporates splitter blades and a vaneless diffuser to maximize efficiency and operating range. These advanced impeller design features are enabled through the use of direct metal laser sintering (DMLS) manufacturing. The resulting design increases the range from 45% to 73% relative to a conventional closed impeller design while maintaining high design point efficiency.

scholarly journals РЕЗУЛЬТАТЫ УСОВЕРШЕНСТВОВАНИЯ СТУПЕНИ ВЫСОКОНАГРУЖЕННОЙ ТУРБИНЫ НИЗКОГО ДАВЛЕНИЯ

2019 ◽  
pp. 30-37
Author(s):  
Игорь Федорович Кравченко ◽  
Сергей Александрович Хомылев
Keyword(s):  
Flow Separation ◽  
Wedge Angle ◽  
Operating Conditions ◽  
Design Flow ◽  
Flow Coefficient ◽  
Low Flow ◽  
Energy Losses ◽  
Suction Surface ◽  
Experimental Development ◽  
Leading Edges

One of the characteristic features of high loaded low-pressure turbine (LPT) with a low flow coefficient is the high-level flow deflection in the blade rows, which have sufficiently thin and strongly curved cross-section profiles. Such profiles are very sensitive to off-design flow angles, especially to positive incidence. Therefore, the effectiveness of a high loaded LPT strongly depends on the working conditions. At the same time, for various reasons, in the process of research tests or operating the engine, the operating conditions may differ greatly from the design ones. Therefore, the creation of a robust LPT design is an actual task. The article considers the computational approbation of the method of increasing the resistance to large off-design angles of attack of vane and blade rows of the intermediate stage of a high loaded LPT of an experimental engine by changing the shape of the leading edges. The turbine was previously tested as part of a full-scale engine, where it was determined that the operating conditions of the LPT and its efficiency are significantly different from the calculated ones. Numerical (CFD) analysis of the flow showed that one of the reasons for the low efficiency is the large angles of attack on the vane and blade rows of the second stage, which lead to the flow separation and an increase of the energy losses coefficients at final. The modernization of the profiles was carried out by reducing the radius and a local increase of the leading edges wedge angle without changing the basic profiles. According to the calculation results, it was allowed to significantly improve the stream. The intensity of the flow deceleration behind the shock wave at the point of transition from the circumference of the edge to the suction surface was reduced, this made it possible to eliminate or reduce the intensity of the flow separation in the vane row and significantly reduce the energy losses coefficient. A more favorable flow was also achieved in the blade row, where a slight decrease in the losses coefficient was also obtained. As a result, the efficiency of the stage and the whole LPT was increased at the off-design operating conditions. This approach can be recommended both to increase the efficiency of the turbine at the experimental development, and when designing new turbines to increase their robustness.

Effect of the Stator Hub Configuration and Stage Design Parameters on Aerodynamic Loss in Axial Compressors

2014 ◽  
Author(s):  
Sungho Yoon ◽  
Rudolf Selmeier ◽  
Patricia Cargill ◽  
Peter Wood
Keyword(s):  
Pressure Loss ◽  
Axial Compressor ◽  
Flow Coefficient ◽  
Design Stage ◽  
Design Parameters ◽  
Leakage Flow ◽  
Design Decision ◽  
Leakage Loss ◽  
Stage Design ◽  
Degree Of Reaction

The choice of the stator hub configuration (i.e. cantilevered versus shrouded) is an important design decision in the preliminary design stage of an axial compressor. Therefore, it is important to understand the effect of the stator hub configuration on the aerodynamic performance. In particular, the stator hub configuration fundamentally affects the leakage flow across the stator. The effect of the stator hub configuration on the leakage flow and its consequent aerodynamic mixing loss with the main flow within the stator row is systematically investigated in this study. In the first part of the paper, a simple model is formulated to estimate the leakage loss across the stator hub as a function of fundamental stage design parameters, such as the flow coefficient, the degree of reaction and the work coefficient, in combination with some relevant geometric parameters including the clearance/span, the pitch-to-chord ratio and the number of seals for the shrouded geometry. The model is exercised in order to understand the effect of each of these design parameters on the leakage loss. It is found that, for a given flow coefficient and work coefficient, the leakage loss across the stator is substantially influenced by the degree of reaction. When a cantilevered stator is compared with a shrouded stator with a single seal at the same clearance, it is shown that a shrouded configuration is generally favored as a higher degree of reaction is selected, whereas a cantilevered configuration is desirable for a lower degree of reaction. Further to this, it is demonstrated that, for shrouded stators, an additional aerodynamic benefit can be achieved by using multiple seals. The second part of the paper investigates the effect of the rotating surfaces. Traditionally, only the pressure loss has been considered for stators. However, the current advanced CFD generally includes the leakage path with associated rotating surfaces, which impart energy to the flow. It is shown that the conventional loss coefficient, based on considering only the pressure loss, is misleading when hub leakage flows are modeled in detail, because there is energy addition due to the rotation of the hub or the shroud seals for the cantilevered stator and the shrouded stator, respectively. The calculation of the entropy generation across the stator is a better measure of relative performance when comparing two different stator hub configurations with detailed CFD.

Efficiency improvement of regenerative pump using blade profile modification: Experimental study

2018 ◽  
Vol 233 (3) ◽  
pp. 448-455 ◽  
Author(s):  
J Nejad ◽  
A Riasi ◽  
A Nourbakhsh
Keyword(s):  
Experimental Study ◽  
Experimental Tests ◽  
Design Flow ◽  
Flow Coefficient ◽  
Low Flow ◽  
Impeller Blade ◽  
Profile Modification ◽  
Compact Size ◽  
Curved Blade ◽  
Regenerative Flow

Regenerative flow pump is a kind of turbomachine with the ability to generate high heads at relatively low flow rates. Despite having low hydraulic efficiency, regenerative pumps have found many applications in industries due to their simplicity, compact size, low manufacturing costs, and low specific speed. In this paper, an experimental study has been carried out to investigate the influence of impeller blade change on the performance of regenerative pump. To this end, the straight radial blades were changed to curved blades with the same inlet/outlet angles. Three forward curved blade impellers as well as straight radial blade impeller were designed and manufactured. Since the regenerative pump comply with the affinity laws, the results of experimental tests were expressed in nondimensional coefficients. The results showed that by increasing the blade angle to 10°, the efficiency increased and at higher blade angles of 30° and 50°, the efficiency decreased for all flow conditions. The best angle was obtained about 15° by curve fitting to the experimental data at the design flow coefficient.

Effects of Inlet Pressure Distortion on the Performance and Flow Field of a Centrifugal Compressor at Off-Design Conditions

2012 ◽  
Author(s):  
N. Sitaram ◽  
M. Govardhan ◽  
K. V. Murali
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
Total Pressure ◽  
Static Pressure ◽  
Design Flow ◽  
Flow Coefficient ◽  
Low Flow ◽  
Performance Measurements ◽  
Perforated Sheet ◽  
Sector Angle

The present paper presents experimental results on the effects of inlet total pressure distortion on the performance and flow field of a centrifugal compressor. The total pressure at inlet is artificially distorted by means of a perforated sheet, which is supported by a support mesh. A total of eleven configurations, including clean inlet configuration, are tested. Performance measurements and impeller inlet and exit flow studies at three flow coefficients, one near design flow coefficient, one below design flow coefficient and one above design flow coefficient, are carried out. The present paper presents and discusses results at off-design flow coefficients and the effects of stage loading on the distortion effects are presented. A new parameter, Distortion Index (DI) is introduced. As DI increases, the mass averaged total pressure at exit stations decreases. Distortion sector angle of 60° having the lowest total pressure is found to be the critical sector for circumferential distortion configurations. As the Distortion Correlation parameter, DC(60) increases, the mass averaged total pressure for circumferential distortion configuration decreases, except in the case of low flow coefficient where DC(60) is nearly constant. DC(60) also increases with sector angle. The static pressure normalized with static pressure for clean inlet decreases as the distortion sector angle is increased. Distortion attenuates the static pressure as the flow passes through the vaneless diffuser. The attenuation increases with the distortion sector angle.

Automatic computational fluid dynamics-based procedure for the optimization of a centrifugal impeller

2005 ◽  
Vol 219 (7) ◽  
pp. 549-557 ◽  
Author(s):  
F Martelli ◽  
S Pazzi ◽  
V Michelassi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
New Technologies ◽  
Geometric Constraints ◽  
Flow Coefficient ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Geometrical Parameters ◽  
Design Point ◽  
Blade Thickness

A typical centrifugal impeller characterized by a low flow coefficient and cylindrical blades is redesigned by means of an intelligent automatic search program. The procedure consists of a feasible sequential quadratic programming algorithm (Fletcher, R. Practical Methods of optimization, 2000 (Wiley)) coupled to a lazy learning (LL) interpolator 1 to speed-up the process. The program is able to handle geometric constraints to reduce the computational effort devoted to the analysis of non-physical configurations. The objective function evaluator is an in-house developed structured computational fluid dynamics (CFD) code. The LL approx-imator is called each time the stored database can provide a sufficiently accurate performance estimate for a given geometry, thus reducing the effective CFD computations. The impeller is represented by 25 geometric parameters describing the vane in the meridional and s-0 planes, the blade thickness, and the leading edge shape. The optimization is carried out on the impeller design point maximizing the polytropic efficiency with nearly constant flow coefficient and polytropic head. The optimization is accomplished by maintaining unaltered those geometrical parameters which have to be kept fixed in order to make the impeller fit the original stage. The optimization, carried out on a cluster of 16 PCs, is self-learning and leads to a geometry presenting an increased design point efficiency. The program is completely general and can be applied to any component which can be described by a finite number of geometrical parameters and computed by any numerical instrument to provide performance indices. The work presented in this paper was done under the METHOD EC funded project for the implementation of new technologies for optimization of centrifugal compressors.

Application of a CFD-Based Program for the Optimization of a Centrifugal Impeller

2003 ◽  
Author(s):  
Simone Pazzi ◽  
Francesco Martelli ◽  
Marco Giachi ◽  
Michela Testa
Keyword(s):  
New Technologies ◽  
Leading Edge ◽  
Computational Effort ◽  
Flow Coefficient ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Geometrical Parameters ◽  
Design Point ◽  
Blade Thickness ◽  
Geometrical Constraints

A typical centrifugal impeller characterized by a low flow coefficient and cylindrical blades is redesigned by means of an intelligent automatic search program. The procedure consists of a Feasible Sequential Quadratic Programming (FSQP) algorithm [6] coupled to a Lazy Learning (LL) interpolator [1] to speed-up the process. The program is able to handle geometrical constraints to reduce the computational effort devoted to the analysis of non-physical configurations. The objective function evaluator is an in-house developed structured CFD code. The LL approximator is called each time the stored database can provide a sufficiently accurate performance estimate for a given geometry, thus reducing the effective CFD computations. The impeller is represented by 25 geometrical parameters describing the vane in the meridional and s-θ planes, the blade thickness and the leading edge shape. The optimisation is carried out on the impeller design point maximizing the polytropic efficiency with more or less constant flow coefficient and polytropic head. The optimization is accomplished keeping unaltered those geometrical parameters which have to be kept fixed in order to make the impeller fit the original stage. The optimisation, carried out on a cluster of sixteen PCs, is self-learning and leads to a geometry presenting an increased design point efficiency. The program is completely general and can be applied to any component which can be described by a finite number of geometrical parameters and computed by any numerical instrument to provide performance indices. The work presented in this paper has been developed inside the METHOD EC funded project for the implementation of new technologies for optimisation of centrifugal compressors.

Effect of the Stator Hub Configuration and Stage Design Parameters on Aerodynamic Loss in Axial Compressors

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Sungho Yoon ◽  
Rudolf Selmeier ◽  
Patricia Cargill ◽  
Peter Wood
Keyword(s):  
Pressure Loss ◽  
Axial Compressor ◽  
Flow Coefficient ◽  
Design Stage ◽  
Design Parameters ◽  
Leakage Flow ◽  
Design Decision ◽  
Leakage Loss ◽  
Stage Design ◽  
Degree Of Reaction

The choice of the stator hub configuration (i.e., cantilevered versus shrouded) is an important design decision in the preliminary design stage of an axial compressor. Therefore, it is important to understand the effect of the stator hub configuration on the aerodynamic performance. In particular, the stator hub configuration fundamentally affects the leakage flow across the stator. The effect of the stator hub configuration on the leakage flow and its consequent aerodynamic mixing loss with the main flow within the stator row is systematically investigated in this study. In the first part of the paper, a simple model is formulated to estimate the leakage loss across the stator hub as a function of fundamental stage design parameters, such as the flow coefficient, the degree of reaction, and the work coefficient, in combination with some relevant geometric parameters including the clearance/span, the pitch-to-chord ratio, and the number of seals for the shrouded geometry. The model is exercised in order to understand the effect of each of these design parameters on the leakage loss. It is found that, for a given flow coefficient and work coefficient, the leakage loss across the stator is substantially influenced by the degree of reaction. When a cantilevered stator is compared with a shrouded stator with a single seal at the same clearance, it is shown that a shrouded configuration is generally favored as a higher degree of reaction is selected, whereas a cantilevered configuration is desirable for a lower degree of reaction. Further to this, it is demonstrated that, for shrouded stators, an additional aerodynamic benefit can be achieved by using multiple seals. The second part of the paper investigates the effect of the rotating surfaces. Traditionally, only the pressure loss has been considered for stators. However, the current advanced computational fluid dynamics (CFD) generally includes the leakage path with associated rotating surfaces, which impart energy to the flow. It is shown that the conventional loss coefficient, based on considering only the pressure loss, is misleading when hub leakage flows are modeled in detail, because there is energy addition due to the rotation of the hub or the shroud seals for the cantilevered stator and the shrouded stator, respectively. The calculation of the entropy generation across the stator is a better measure of relative performance when comparing two different stator hub configurations with detailed CFD.

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